The resident mitochondrial protein kinases (mPKs) comprising pyruvate dehydrogenase kinases (PDKs), and branched-chain 1-ketoacid dehydrogenase kinase (BCK) are the molecular switches that control carbohydrate and branched-chain amino acid degradation. Mitochondrial PDKs (isoforms 1, 2, 3 and 4) down-regulate activity of the mitochondrial pyruvate dehydrogenase complex by reversible phosphorylation, in response to hormonal and nutritional stimuli. Certain PDK isoforms are over-expressed in disease states such as type 2 diabetes, obesity and cancer, resulting in decreased glucose oxidation. Towards understanding the structure and function of these PDKs, the P.I.'s laboratory has solved the crystal structures for three (PDK1, PDK3 and PDK4) of the four PDK isoforms and various PDK-inhibitor/activator complexes. Based on these advances, the P.I. proposes to continue investigation into the structure, function and regulation of mammalian PDKs. The Specific Aims are: 1) To decipher the allosteric mechanisms by which the L2 domain and the synthetic ligands modulate PDK activities; 2) To offer biochemical and structural basis for the hyperactivity of PDK4 and to identify the E1p substrate-binding site in this kinase isoform; 3) To isolate a new generation of small-molecule inhibitors that are specific for PDK4 by high-through-put screening and characterize these novel inhibitors both in vitro and in cell culture. Standard methods including X-ray crystallography, isothermal titration calorimetry, kinase activity assays and the high-through-put screening method will be employed to achieve these Specific Aims. The availability of PDK4-specific inhibitors will foster new strategies to mitigate defective glucose oxidation in obesity and type 2 diabetes.